The present invention pertains to a sewing machine with a needle bar which can be moved up and down with a thread-guiding needle, with a thread take-up lever, at least one thread-tensioning device, with a pressure bar which can be moved up and down between an inoperative position and a pressing position with a presser foot which can be lowered onto a fabric support surface, with a shuttle, which is arranged under the fabric support surface and cooperates with the needle, with a thread-cutting device provided at least for cutting the needle thread and with a device for pulling away the reserve-side needle thread end, which can be actuated after the thread-cutting operation.
When the presser foot of the sewing machine is lowered onto the fabric before the beginning of a sewing operation, the thread end hanging down from the needle should not be located under the presser foot because there is otherwise a risk that the thread end is jammed between the presser foot and the fabric. The consequence of this would be that the thread end could not be pulled to the underside of the fabric at the beginning of the sewing operation but would remain on the top side as a sticking-out thread end impairing the appearance of the seam.
To prevent this, it has been known, e.g., from DE 25 26 694 C2 (U.S. Pat. No. 3,901,171) that the needle thread end is moved out of the area of the presser foot by means of a take-up sweep assembly designed as a thread sweep, which is moved through between the presser foot and the needle. Such take-up sweep assemblies operate very reliably and are therefore frequently used. However, their use is limited during the processing of very thick materials, e.g., padding, because the distance between the presser foot and the needle, which is in the raised position, may be so narrow that no sufficient space is available for the passage of the thread sweep.
In contrast, such take-up sweep assemblies, in which the needle thread end is moved out of the area of the presser foot by a compressed air stream rather than by a mechanical thread sweep, can be used during the processing of thick materials. Such a take-up sweep assembly has been known, e.g., from U.S. Pat. No. 3,371,632. However, such means are disadvantageous compared with mechanically operating means because resistant threads, which may additionally also be twisted, may sometimes be pulled away from the area of the presser foot only insufficiently and the means also have a comparatively high compressed air and consequently energy consumption.
The basic object of the present invention is to provide a take-up sweep assembly which can be used for processing both thin and especially thick materials without limitations.
According to the invention, a sewing machine is provided with a needle bar which can be moved up and down with a thread-guiding needle, with a thread take-up lever, with at least one thread-tensioning device, with a pressure bar which can be moved up and down between an inoperative position and a pressing position with a presser foot which can be lowered onto a fabric support surface and with a shuttle, which is arranged under the fabric support surface and cooperates with the needle. A thread-cutting device is provided at least for cutting the needle thread. A device for pulling away the reserve-side needle thread end, which device can be actuated after the thread-cutting operation is also provided. The device for pulling away the needle thread end is formed by a pin, which extends at right angles to the path of the needle thread. The pin extends between two thread guides and can be moved essentially at right angles through the path of the needle thread between an inoperative position and a functional position. The movement of the pin from the inoperative position into the functional position takes place after a thread-cutting operation. The thread-tensioning device is put in operation and moved back into the inoperative position before a repeated sewing start.
The present invention is based on the idea that the needle thread end is retracted through the eye of the needle by the pin, which can be moved at right angles to the path of the needle thread, just so much that the presser foot cannot be jammed between the presser foot and the fabric during the lowering of the thread end, on the one hand, and the thread end hanging down from the eye of the needle still has a sufficient length for satisfactory thread knotting at the beginning of the next sewing operation. One essential requirement for reliable thread knotting is that the retracted amount of thread is released before the next start of sewing and is thus available as a free thread reserve.
A take-up sweep assembly which also has a thread retracting pin movable at right angles to the path of the needle thread besides a thread sweep has been known from DE-GM 75 01 449 (U.S. Pat. No. 3,847,102). This thread retracting pin, which can be moved simultaneously with the thread sweep, supports the action of the thread sweep, which performs only a comparatively small pivoting movement, by additionally retracting a small amount of thread through the eye of the needle. Since this thread retracting pin is thus used only as an auxiliary means, the thread sewing machine has besides a thread pull-away mechanism proper, namely, the thread sweep, by shortening the thread end that may not have been removed far enough from the presser foot by the thread sweep to the extent that it cannot be jammed under the presser foot any more, the DE-GM could not have suggested the inventive idea, namely, the provision of a take-up sweep assembly that has only a thread retracting pin.
The fact that the measure according to the present invention, namely, the prevention of the jamming of the needle thread end solely by shortening the thread end, cannot have been obvious arises especially from the fact that DE-OS 1 933 780 (U.S. Pat. No. 3,540,235) and DE 22 07 366 B2 (U.S. Pat. No. 3,695,200) propose that an additional thread reserve be made available for reliable thread knotting at the beginning of the next sewing operation in case of the use of a thread sweep, even though the length of the thread end hanging down from the eye of the needle remained unaffected by a thread sweep and the thread knotting at the beginning of the next sewing operation is therefore not compromised. This thread reserve is produced by the fact that a thread pull-off pin which can be moved at right angles to the needle thread pulls off a certain amount of thread before the thread cutting from the thread reserve through the opened thread-tensioning device and releases it again before the next start of sewing.
The invention may be employed with an angle lever having one arm which carries the pin and another arm which is connected to a drive arranged within the head cover. The angle lever may be mounted on a bolt arranged on the head cover of the machine housing.
The drive may be arranged on a carrier fastened adjustably within the head cover. A compressed air cylinder or an electromagnet may be used as the drive.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its uses, reference is made to the accompanying drawings and descriptive matter in which a preferred embodiment of the invention is illustrated.